The purpose of this proposal is to develop a platform technology for the identification of targeting ligands for gene therapy. The novel system described here called LIVE (Ligand Identification Via Expression) uses genetic selection to identify phage that display gene targeting ligands. It differs significantly from previous phage display techniques in that selection is base on a genetic change in the target cells (for example the introduction of a green fluorescent reporter gene) rather than selection based on simple affinity interactions. In this proposed study, we will develop improved methods of LIVE selection and improved phage libraries of both natural and synthetic peptides. The libraries will be selected for functional ligands that target pancreatic islet cells in-vivo and in-vitro. The efficacy of these new targeting ligands will be assessed by using the phage itself as the gene delivery vehicle. We will also assess the applicability of LIVE to the discovery of ligands for various receptor types by testing the ability of various ligand targeted phage to transduce receptor bearing cells with a GFP reporter gene. Thus the technology developed here will have immediate applications to the treatment of diabetes by targeted gene therapy and more broadly as a proven platform technology for ligand, gene, and peptide discovery. PROPOSED COMMERCIAL APPLICATIONS: We propose to develop a novel platform technology for identifying gene targeting ligands with immediate application to the treatment of diabetes by targeted gene therapy. The technology called LIVE will serve as a platform for the discovery of new targeting ligands for existing gene therapy vectors and for the use of phage themselves as vectors for both ex-vivo and in-vivo gene therapy. In addition, the technology is also a functional genomics platform for discovery of previously uncharacterized ligands for specific cell types. The cDNA library construction and selection technology developed here is directly applicable to the discovery of paracrine and autocrine ligands.